Air pollution can intensify Covid-19
As India faces a steep rise in Covid-19 cases, it is critical to employ all reasonable strategies to decrease transmission and to lower the number of severe infections which burden the health care system. Reducing air pollution is one such strategy that may be more important for India than any other country globally. So far, the spread of the pandemic has occurred during spring and summer when air pollution is relatively mild, but the interaction of high winter pollution levels with Covid-19 infections can have serious consequences.
India has some of the highest exposures to air pollution in the world and faces a double impact from outdoor air pollution in cities and throughout the Indo-Gangetic Plain, plus household air pollution from the millions of chulhas in daily use especially in rural areas. Covid-19 is a respiratory infection, and we know from other such infections that air pollution can worsen their severity through its impact on the immune response. In 2019, nearly 200,000 respiratory infection deaths in India were linked to air pollution exposure. Simply put, air pollution may be an important factor that moves a mild Covid-19 infection to one that requires acute medical care.
Although direct evidence of the impact of air pollution on Covid-19 is limited, and more time will be needed to conduct proper studies, evidence from the SARS epidemic in 2003 (caused by a similar virus) indicated a link between air pollution and increased mortality. Evidence from multiple countries, including studies from India, shows consistent associations between both short-term exposure to air pollution and hospitalisation for pneumonia infections (in children), and between long-term exposure and several types of respiratory infections in children.
Studies of short-term increases in air pollution suggest a worsening severity of co-incident respiratory infections. This co-exposure interaction is supported by mechanistic studies which show how air pollution reduces the immune response to respiratory infections. For example, in the lower airways, where respiratory infections are most damaging, immune cells called macrophages can digest and destroy viruses and bacteria, but under conditions of air pollution exposure, these cells become filled up with particles and are no longer effective against the infection. Emerging research also suggests the air pollution may alter lung cells to increase the number of Sars-CoV-2 virus receptors.
In addition, another group of studies indicates that longer-term exposure to air pollution increases the risk of infections, especially in those with pre-existing chronic lung disease. In this case, air pollution can lead to permanent structural changes in the lungs that erode a person’s reserves. An infection that might lead to mild symptoms in a healthy person results in severe impact in those with chronic lung disease. This may be one reason that many of the same diseases caused by air pollution are also present in the majority of people with Covid-19 infections severe enough to require hospitalisation.
Along with these roles in increasing susceptibility to infections and worsening infection severity, some reports also suggest a role of air pollution in increasing transmission of the virus. Studies have detected the presence of the virus on air pollution particles, but this does not mean these particles are themselves infectious and current evidence does not suggest that the virus hitching a ride on air pollution particles is an important route of transmission. Further, there is little evidence to indicate that infections occur outdoors except when people are in very close proximity. Although there is no direct evidence, there is a plausible pathway by which air pollution may enhance transmission by making it more likely that an infected individual will cough.
So, what does this all mean for India? From one perspective, the current timing of the pandemic in India during the months of the year when air pollution is at its lowest levels suggests a window of opportunity during which concerted actions to reduce virus transmission may be effective in “flattening the curve”.
However, timing is important, as winter typically brings much higher levels of air pollution and the potential for the interaction with Covid-19 infections to lead to far larger impacts. Thus it is critical, even as economic activity increases, to accelerate the air pollution control measures already described in the National Clean Air Programme.
Actions such as agricultural (stubble) burning that may lead to episodes need to be either curtailed entirely or managed in a way that is timed with tightening of pandemic management measures. In the future, full-scale lockdowns are unlikely, but may be replaced by on-again/off-again measures that could be targeted towards periods of high and low air pollution, to balance Covid-19 cases and air pollution against economic activity and employment. More rapid expansion of LPG use may reduce household pollution.
There has never been a more important time for action on air pollution. Efforts implemented today will have immediate impact related to Covid-19 and will also continue to bear dividends long into the future via benefits on diabetes and chronic heart and lung diseases. What’s more, actions taken to improve air quality will benefit everyone.